The art has long sought simple, economical, and effective means for determining the condition of oils. It has long been recognized that the degradation of oils involves the oxidation of the oil's various components. This process involves chemical changes in the composition of the oil leading to an increase ultimately in the acidity of the oil. Another factor is the contamination of the oil with water, acid and sludge which result primarily from piston ring and valve guide blow-by. Together these two factors ultimately produce acidic oil which should be changed.
There is not available, however, a satisfactory monitoring apparatus which will monitor the engine oil to determine when the oil has degraded sufficiently to the point where the oil should be changed. So far as is known, the usual prior art method for testing the lubrication oil has consisted of obtaining a sample of the oil and transporting this sample to a laboratory for analysis. While such a method can correctly analyze the oil to determine numerous art recognized factors, such as flash point, pour point, ppm of wear metals, viscosity, sulfated ash content, TBN and TAN, the time delays involved in obtaining results make this method unsatisfactory for determining oil change times, particularly when the engine is located at a remote location from the laboratory.
One standard method for determining the acidity of oil is set forth in the American Society of Testing Materials Standard Test Method D 974. This is also a standard of the Institute of Petroleum under the designation IP 139. This titration method has been widely used to indicate the relative changes that occur in an oil during use under oxidizing conditions and reports these changes in terms of relative changes in neutralization numbers known as the Total Acid Number (TAN) and the Total Base Number (TBN). Compounded engine oils can and usually have both acid and base numbers in this test.
The field of this invention is the detection of the formation of organic acids during the degradation of a lubricant. The kind of detection involved is colorimetric reaction produced by a chromogen the color change of which depends on the buildup of organic acids within the lubricant. Such detectors can be qualitatitive, semi-qualitatitive, or quantitative, and can be read with standard reflectance spectrophotometers, or visually by the eye using color comparison standards. Remote optical sensing of degradation of oil within an operating machine is feasible through the use of a light source and detectors connected via light fibers to the colorimetric detector of this invention. Optical techniques of this type are illustrated in Heitzman U.S. Pat. No. 4,557,900. The invention here relates to the novel chemistry of the detector, and its method of preparation and use.
The subject invention provides a method and apparatus for directly monitoring the corrosive tendency of the oil through visual observations of the changes in color and fluorescence of dyed and chemically treated polymer matrices which have been placed in contact with the oil to be monitored. The method does not require a laboratory or sophisticated chemical equipment, training or skills. The method can be used both as an indicator that the oil should be changed and as a basis to determine, in the field, whether or not a lubricating oil is the wrong type for the engine. With the present invention, mere guesswork is not involved in determining the precise point when a lubricating oil should be changed.